The increase is due to supply constraints, rising input costs, and the ongoing trade dispute between the two countries, the Boston-based green-energy consultancy said in a report.

Chinese-made modules are significantly cheaper than those made in other areas, and GTM Research estimated they were 55% of total modules shipped to the U.S. last year.

Chinese firms are quoting modules at 80 cents to 85 cents per watt for delivery in the second half of the year, compared to 70 cents per watt at the end of 2013, the report said.

The ongoing U.S.-China trade case is the "primary driver" behind the price increase, the report said.

More duties on Chinese and Taiwanese solar modules would push up U.S. pricing beyond current levels, as the firms would pass on tariff-induced penalties onto customers or contract out cell and module production to vendors based in higher-cost countries such as India, South Korea, and Malaysia, GTM Research said.

The U.S. began investigating earlier this year allegations that solar-panel manufacturers in China and Taiwan could be evading duties.

Cheap and plentiful solar panels from China have fueled the boom in rooftop solar systems, and analysts at Cowen and Co. have said U.S. solar-panel manufacturing capacity is so constrained that U.S. manufacturers are unlikely to reap benefits from any potential trade barriers.

Meanwhile, shares of most solar companies endured another day of losses.

Shares of manufacturer and solar developer First Solar Inc. FSLR -4.94% were down 4%. Shares of solar installer SolarCity Corp. SCTY -4.00% declined 1.2%. Canadian Solar Inc. CSIQ -10.39% was among the top decliners, with shares falling 7.8%.